the contact lens exam
Don't Let Early Studies Sway You From Using New Technology
BY LORETTA B. SZCZOTKA-FLYNN, OD, MS, FAAO
During your contact lens exam, do you routinely think about putting your problem patients into the newest lenses? For example, do you consider refitting patients who have chronic red eyes into silicone hydrogel lenses? Do you consider daily disposables for patients who are noncompliant or complain of chronic discomfort? Such methods are based on sound judgement and from learning about the science and benefits of new lens materials.
However, such methods may also be leading to unusually high adverse response rates in the epidemiological studies performed relatively soon after new modalities enter the market.
Two large-scale epidemiological studies have just been released on the risk of microbial keratitis (MK) with modern modes of contact lens wear. In two companion studies in the October 2008 Ophthalmology, Stapleton and colleagues in Australia and Dart and colleagues in the United Kingdom documented the risk of MK with daily and extended wear of various lens materials. Silicone hydrogel and daily disposable lenses were included and compared to soft hydrogels.
One important take-home message from these papers is that the risk of MK with extended wear lenses has not changed over the past 20 years compared to the 1989 reports from Schein and Poggio, which assessed annual or disposable low-Dk lens wear only. The risk remains at about 20 per 10,000 extended wear users (or about 1 per 500 extended wear users).
However, in the recent Australian and UK papers, daily disposables and silicone hydrogel daily wear have not reduced MK and in some cases demonstrated surprisingly high rates of MK. Specifically, Dart reported that daily disposables had a 1.56 times greater risk of MK compared to planned replacement soft lenses, and Stapleton reported that the risk of MK with silicone hydrogel daily wear was 11.9 per 10,000 users compared to 1.9 per 10,000 users of daily wear soft hydrogels.
Time Will Tell
Early adopters of new technology may contribute to the increased risk seen in these population-based studies of newer lens types. Keay and colleagues (2007) have shown that an early excess risk of MK in frequent replacement lens wearers — which was first reported between 1992 and 1998 — is no longer evident in contemporary studies where these lenses are now widely used in the community. This suggests that patients put into the latest technology in the early studies were unique in terms of risk taking behaviors or were fitted into the frequent replacement modality because of poor success with conventional lens wear.
Thus, the unchanged risk of MK or the unusually high rate of MK with silicone hydrogel daily wear noted in the Australian study may in fact diminish over time as silicone hydrogel lenses and daily disposable lenses account for a greater percentage of lenses prescribed in the population.
So the next time you examine a contact lens patient who has frequent complaints, keep an open mind. Chronically red eyes may result from hypoxia, but they may also be due to dry eyes, allergies or underlying lid or systemic disease. Chronic contact lens discomfort may result from dry eyes, lid disease, allergies, hypoxia or occupational conditions. Try the newest and greatest products; they may solve the problem, but don't be disheartened if some patients just aren't suited for contact lens wear. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #157.
Dr. Szczotka-Flynn is an associate professor at Case Western Reserve University Dept. of Ophthalmology and is director of the Contact Lens Service at University Hospitals of Cleveland.